1. Field of the Invention
This invention relates to a compound bearing assembly for supporting a swing arm of a hard disc drive.
2. Description of the Prior Art
A prior art hard disc drive as shown in FIG. 4 comprises a magnetic disc 11 which is driven for rotation by a motor M, and a swing arm (or head arm) 13 carrying at the end thereof a magnetic head 12 for writing data in the disc 13 at a predetermined position thereof and reading out data from the disc 13 at a given position thereof.
The swing arm 13 has a base part rotatably supported by a compound bearing assembly which uses two ball bearing units. As shown in FIG. 6, a prior art bearing assembly for supporting the swing arm comprises two ball bearing units A and B and a sleeve-like spacer C. These components of the bearing assembly are produced separately and supplied to the user, i.e., the hard disc drive manufacturer or the swing arm manufacturer, to be assembled on a shaft D.
In other words, with the conventional swing arm support bearing assembly, the user has to assemble the two ball bearing units on the shaft via the spacer. This poses the following problems.
(a) The shaft has to be sized in its production to the inner diameter of the inner race rings of the ball bearing units. In addition, its rigidity is subject to restrictions.
(b) The spacer should have highly accurate parallelism between and flatness of its opposite end finished surfaces.
(c) It is necessary to provide uniform contact between the opposite end surfaces of the spacer and the corresponding end surfaces of the outer race rings of the ball bearing units, thus requiring highly accurate finishing.
(d) For the above reasons, the assembling by the user cannot be easily done.